Was Plato a Pythagorean? The question is not simple. It turns on what one makes of the term Pythagorean and how one reads Plato. Since neither of these factors are simple or self-evident, the relation between the two is hard to determine, and any assessment of it is bound to provoke debate. Ancient Pythagorean roots are welcomed by Plato's own philosophy, and then reinterpreted by the Academy, which keep engaging with the Pythagorean epistemological and metaphysical effort. This is particularly true if one look at Plato’s theories of the soul. Although the Pythagoreans are probably to most immediate source of Plato’s original assessment of the immortality of the soul, the final complex theory of the soul in platonic dialogues is mostly the outcome of Plato’s philosophical outlook. Indeed, Plato’s theory of the soul is developed entirely within the full scope of Plato's theoretical philosophy. Despite recognizing the Pythagorean influence in the theory of the soul, one must admits that Plato develops the argument in a fairly novel way. The methodological adoption by Plato of previous Pythagorean doctrines corresponds to a first movement of that beautiful path that we have called elsewhere the Platonic mediation (or conciliation) of Pythagoreanism (Cornelli 2013). This is especially true regarding the theory of the soul. At the same time Plato seems to rely on several orphic materials to build up important pieces of his theories: an historiographical, philological and philosophical operation that was famously called transposition by Diès (1927). This Course will therefore explore the Orphic-Pythagorean, religious and philosophical, sources that underlie Plato's ethical and epistemological theories of the soul, with special attention to Plato’s dialogues Phaedo, Meno, Republic and Philebus.